This application focuses on CAML (Calcium Modulating cyclophilin Ligand), an intracellular, integral membrane protein. The applicant seeks to learn how it participates in the functions of the Epidermal Growth Factor Receptor (EGFR) and to determine its role in EGFR-mediated neoplastic transformation. The EGFR (also known as ErbB1) is important for many different processes, including morphogenesis, wound healing, and gut integrity through its effects on cell proliferation, differentiation, migration, and survival. It is also a frequent target of amplification and inappropriate activation in a large proportion of human cancers. The applicant has recently discovered that CAML forms a complex with the cytoplasmic tail of the EGFR in vitro and in intact cells. Cells engineered to lack the CAML gene have severely impaired proliferative responses to EGF. These cells have a specific defect in the ability of EGFR to recycle back to the plasma membrane following EGF-induced receptor internalization. These data lead to the central hypothesis that CAML is required for long-term proliferative responses mediated by the EGFR, through regulation of receptor recycling. Given the significance of EGFR in genesis and treatment of cancers, it is essential to understand the mechanisms underlying its biological effects. In addition, CAML or related cellular components that specifically function in the process of receptor trafficking may turn out to be useful as molecular targets for cancer therapy. Specific aims in this project will focus on 1) identification of protein domains that mediate interaction of EGFR and CAML;2) the role of interaction between CAML and the cytoskeleton, as a possible mediator of its effects on the EGFR;3) elucidation of the mechanism by which CAML regulates EGFR recycling;and 4) identification of the role of CAML in normal and oncogenic functions of the EGFR using a conditional knockout mouse model.